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The above poster means Aquarium Salt - you do not want to add table salt.

Thanks, i'll get some aquarium salt. It seems fairly inexpensive so I think it makes sense to get it from a pet shop rather than buy online and pay postage.

Also, I am wondering how to maintain the temperature in my tank. I don't have a heater (this is something I presumed I wouldn't need for a cold water tank) so i'm not sure how to maintain a 20-22 degrees temperature in my tank. Over the course of around 20hrs it has dropped back down to 17 degrees celsius.

I have no heater, i've never had one. My 5 y.o goldie has never been in a tank with a heater, as, i'd imagine, my 3 month old shub.

I'm waiting on my API tester kit coming so hopefully that will show something up in the water that can help me to solve the apparent illness of my goldie, however do you think I _need_ a heater? It is a coldwater tank after all and I have never needed a heater before.

Also, i've just done my third daily water change in a row so i'm hoping that I will see a upturn in my goldie's health soon and that his fins will sort of open back up rather than being in the clamped state they are in just now.

I have now managed to get my water tested with my API freshwater test kit and these are the results:

pH - 7.6 (light blue and end of the scale)
pH (High Range) - 7.4 (tan colour and top of the scale)
Ammonia - 0.25ppm (light green and second in the scale)
Nitrite - 0ppm (light blue and top of scale)
Nitrate - 10ppm (light orange and third in scale)

Should I be concerned about any of these figures?

Do any of these figures point me in the direction of the reason for my fish suffering from clamped fins and showing "hiding" behaviour?

I should add that I haven't done a water change since Saturday/Sunday.

Parameters are fine, though ammonia is slightly higher than it should be.

You say it stays around 12-15 C ... that is around 53-59 F ... which is the low end of what goldfish tend to prefer, unless its a fancy goldfish, which should really be higher than that. The chub should be fine, though less active than normal.

If you do not wish to buy a heater, bring up and maintain the ambient room temperature.